Effect of methylamine and monodansylcadaverine on the susceptibility of McCoy cells to Chlamydia trachomatis infection

The immunobiology of Chlamydia

Bacteria of the genus Chlamydia cause a wide variety of disorders in animals and people worldwide. The immune response to chlamydiae is poorly understood and, as Daniel Levitt shows here, there is recent evidence that these organisms induce perturbations in immune function that may assist their own survival in infected hosts and that of co-infecting microbes.

Targeting aminopeptidase N, a newly identified receptor for F4ac fimbriae, enhances the intestinal mucosal immune response

Enterotoxigenic Escherichia coli (ETEC) are a major cause of diarrhea in human and animal. In piglets, ETEC having F4 fimbriae (F4(+) ETEC) induce severe diarrhea, dependent on the presence of receptors for F4 (F4R). In this study, porcine aminopeptidase N (pAPN) was identified as an F4R by comparative proteomic analysis of brush border proteins of F4R(+) and F4R(-) pigs and by adherence/internalization experiments on pAPN-transfected cells. Binding of F4 fimbriae to pAPN depended on sialic acid containing carbohydrate moieties, and resulted in clathrin-mediated endocytosis of the fimbriae. Endocytosis via pAPN was not restricted to F4 fimbriae, but was also observed for anti-pAPN antibodies. Both F4 fimbriae- and pAPN-specific antibodies were taken up in vivo by porcine enterocytes and induced subsequently a rapid immunoglobulin A and G response. In conclusion, we identified pAPN as an endocytotic receptor for F4 fimbriae and highlight the opportunity to target vaccine antigens to this epithelial receptor.

Clathrin-mediated endocytosis and transcytosis of enterotoxigenic Escherichia coli F4 fimbriae in porcine intestinal epithelial cells

Enterotoxigenic Escherichia coli (ETEC) cause severe diarrhea in neonatal and recently weaned piglets. Previously, we demonstrated that oral immunization of F4 receptor positive piglets with purified F4 fimbriae induces a protective F4-specific intestinal immune response. However, in F4 receptor negative animals no F4-specific immune response can be elicited, indicating that the induction of an F4-specific mucosal immune response upon oral immunisation is receptor-dependent. Although F4 fimbriae undergo transcytosis across the intestinal epithelium in vivo, the endocytosis pathways used remain unknown. In the present study, we characterized the internalization of F4 fimbriae in the porcine intestinal epithelial cell line IPEC-J2. The results in the present study demonstrate that F4 fimbriae are internalized through a clathrin-dependent pathway. Furthermore, our results suggest that F4 fimbriae are transcytosed across differentiated IPEC-J2 cells. This receptor-dependent transcytosis of F4 fimbriae may explain the immunogenicity of these fimbriae upon oral administration in vivo.

The PilC adhesin of the Neisseria type IV pilus - binding specificities and new insights into the nature of the host cell receptor

Type IV pili of Neisseria gonorrhoeae and Neisseria meningitidis mediate the first contact to human mucosal epithelial cells, an interaction which is also critical for the interaction with vascular endothelial cells. The PilC proteins have been characterized as the principal pilus-associated adhesin. Here we show that PilC2 exhibits a defined cell and tissue tropism, as it binds to human epithelial and endothelial cell lines, but not to human T cells or fibroblasts. Piliated gonococci and PilC2 exhibit similar patterns of binding to human epithelial and endothelial cells, supporting the function of PilC as the key pilus adhesin. Although CD46 has previously been suggested to be a pilus receptor, several observations indicate that neisserial type IV pili and the pilus adhesin PilC2 interact with epithelial cells in a CD46 independent manner. Biochemical approaches were used to characterize the nature of host cell factors mediating binding of piliated gonococci and PilC2 protein. Our data indicate that the putative host cell receptor for gonococcal pili and the PilC2 pilus adhesin is a surface protein. Glycostructures were found to not be involved in binding. Moreover, we observed the uptake of purified PilC2 protein together with its receptor via receptor-mediated endocytosis and subsequent receptor re-exposure on the cell surface. Our data support the existence of a specific pilus receptor and provide intriguing information on the nature of the receptor.

Receptor-mediated endocytosis of Neisseria gonorrhoeae into primary human urethral epithelial cells: the role of the asialoglycoprotein receptor

Urethral epithelial cells are invaded by Neisseria gonorrhoeae during gonococcal infection in men. To understand further the mechanisms of gonococcal entry into host cells, we used the primary human urethral epithelial cells (PHUECs) tissue culture system recently developed by our laboratory. These studies showed that human asialoglycoprotein receptor (ASGP-R) and the terminal lactosamine of lacto-N-neotetraose-expressing gonococcal lipooligosaccharide (LOS) play an important role in invasion of PHUECs. Microscopy studies showed that ASGP-R traffics to the cell surface after gonococcal challenge. Co-localization of ASGP-R with gonococci was observed. As ASGP-R-mediated endocytosis is clathrin dependent, clathrin localization in PHUECs was examined after infection. Infected PHUECs showed increased clathrin recruitment and co-localization of clathrin and gonococci. Preincubating PHUECs in 0.3 M sucrose or monodansylcadaverine (MDC), which both inhibit clathrin-coated pit formation, resulted in decreased invasion. N. gonorrhoeae strain 1291 produces a single LOS glycoform that terminates with Gal(beta1-4)GlcNac(beta1-3)Gal(beta1-4)Glc (lacto-N-neotetraose). Invasion assays showed that strain 1291 invades significantly more than four isogenic mutants expressing truncated LOS. Sialylation of strain 1291 LOS inhibited invasion significantly. Preincubation of PHUECs in asialofetuin (ASF), an ASGP-R ligand, significantly reduced invasion. A dose-response reduction in invasion was observed in PHUECs preincubated with increasing concentrations of NaOH-deacylated 1291 LOS. These studies indicated that an interaction between lacto-N-neotetraose-terminal LOS and ASGP-R allows gonococcal entry into PHUECs.

Optimal development of Chlamydophila psittaci in L929 fibroblast and BGM epithelial cells requires the participation of microfilaments and microtubule-motor proteins

The cytoskeleton is involved in several cellular activities, including internalization and transport of foreign particles. Although particular functions to each cytoskeleton component have been described, interactions between those components seem to occur. The involvement of the different host cell cytoskeletal components in uptake and development of Chlamydophila psittaci is incompletely understood. In this study, the participation of the microfilament network along with the kinesin and dynein microtubule motor proteins in the internalization and further development of Chlamydophila psittaci were investigated in L929 fibroblast and BGM epithelial cells. Cytochalasin D disruption of actin filaments, and blockage of the motor proteins through the introduction of monoclonal antibodies into the host cells were carried out, either single or combined, at different moments around bacterial inoculation, and Chlamydophila infectivity determined 24 h post- inoculation by direct immunofluorescence. Our results show that, although Chlamydophila Ipsittaci can make use of both microfilament-dependent and independent entry pathways in both cell types, Chlamydophila internalization and development in the fibroblast cells mainly concerned processes mediated by microfilaments while in the epithelial cells mechanisms that require microtubule motor proteins were the ones predominantly involved. Evidence that mutual participation of the actin and tubulin networks in both host cells are required for optimal growth of Chlamydophila psittaci is also presented.

Localization of intracellular Ca2+ stores in HeLa cells during infection with Chlamydia trachomatis

Chlamydia trachomatis elementary bodies (EBs) enter epithelial cells within membrane-bound endosomes that aggregate with each other in a calcium-regulated process, but avoid fusion with lysosomes. Annexin III but not I translocates to chlamydial aggregates and inclusions. In this study, we localize the intracellular Ca2+ stores during the course of infection by analyzing the distribution of three intracellular Ca2+ store proteins: calreticulin, type-1 inositol-1,4, 5-trisphosphate receptor (IP3-R), and Sarcoplasmic/Endoplasmic Reticulum Ca2+ ATPase type 2 (SERCA2) in HeLa cells infected with C. trachomatis serovar L2. In uninfected cells, immunofluorescence staining of the proteins showed a fine granular distributed pattern for all three proteins. After infection with C. trachomatis, calreticulin was found at the periphery of chlamydial aggregates and inclusions from 3 to 48 hours post-infection. In infected cells, SERCA2 was intimately associated with chlamydial inclusions after 3 and 24 hours, but not after 48 hours. Moreover, IP3-R was translocated to and colocalized with EB aggregates and chlamydial inclusions and had a distribution very similar to that of SERCA 2. After 24 hours incubation with chlamydiae, there was a local accumulation of [Ca2+]i (105+/-17 nM) in the proximity of chlamydial inclusions, compared to 50+/-13 nM in other parts of the cell cytoplasm. In the absence of extracellular Ca2+, this local accumulation of Ca2+ increased to 295+/-50 nM after adding 50 microM ATP, and to a similar extent after adding 100 nM thapsigargin (Tg). These data indicate that during infection of HeLa cells with chlamydiae, intracellular Ca2+ stores are redistributed, causing local accumulation of Ca2+ in the vicinity of chlamydial inclusions. These changes may trigger the association of certain proteins such as annexins with chlamydia-containing vesicles, and thereby regulation of membrane-membrane interaction during endosome aggregation and inclusion formation.

Entry and intracellular localization of Legionella dumoffii in Vero cells

Organisms of some Legionella species are known to internalize and multiply within epithelial cell lines. During the study on interaction between Legionella spp. and Vero cells, we found that L. dumoffii Tex-KL (ATCC 33343) can enter into Vero cells approximately four to 20 times more often than five other strains of four species of legionella. The mode of entry between L. dumoffii Tex-KL and L. pneumophila Philadelphia-1 was compared and studied by treating Vero cells with reagents which inhibit phagocytosis and endocytosis. Monodansylcadaverine, cytochalasin D and nocodazol were used as inhibitors of receptor-mediated endocytosis, microfilament-dependent phagocytosis and polymerization of microtubules, respectively. The uptake of L. dumoffii Tex-KL required receptor-mediated endocytosis by Vero cells, while the uptake of L. pneumophila Philadelphia-1 used mainly microfilament-dependent phagocytosis. Polymerization of microtubules was necessary for Vero cells for the uptake of both strains of legionella. An electron microscopic examination revealed that some organisms of the L. dumoffii strain Tex-KL escaped from endosomal vacuoles into cytoplasm in the early stage of infection, and proliferated in the cytoplasm. At that period, most of the bacteria were surrounded by rough endoplasmic reticula. In contrast, L. pneumophila Philadelphia-1 proliferated only within ribosome-lined endosome. We suggest that L. dumoffii Tex-KL internalize and proliferate in Vero cells in a different way to L. pneumophila Philadelphia-1, and that there is a variety of the mode of interaction between Legionella spp. and epithelial cells.

Safe haven: the cell biology of nonfusogenic pathogen vacuoles

Our understanding of both membrane traffic in mammalian cells and the cell biology of infection with intracellular pathogens has increased dramatically in recent years. In this review, we discuss the cell biology of the host-microbe interaction for four intracellular pathogens: Chlamydia spp., Legionella pneumophila, Mycobacterium spp., and the protozoan parasite Toxoplasma gondii. All of these organisms reside in vacuoles inside cells that have restricted fusion with host organelles of the endocytic cascade. Despite this restricted fusion, the vacuoles surrounding each pathogen display novel interactions with other host cell organelles. In addition to the effect of infection on host membrane traffic, we focus on these novel interactions and relate them where possible to nutrient acquisition by the intracellular organisms.

Invasion of cultured human epithelial cells by Klebsiella pneumoniae isolated from the urinary tract

The mechanisms which enable entry into cultured human epithelial cells by Klebsiella pneumoniae were compared with those of Salmonella typhi Ty2. K. pneumoniae 3091, isolated from a urine sample of a patient with a urinary tract infection, invaded human epithelial cells from the bladder and ileocecum and persisted for days in vitro. Electron microscopic studies demonstrated that K. pneumoniae was always contained in endosomes. The internalization mechanism(s) triggered by K. pneumoniae was studied by invasion assays conducted with different inhibitors that act on prokaryotic and eukaryotic cell structures and processes. Chloramphenicol inhibition of bacterial uptake revealed that bacterial de novo protein synthesis was essential for efficient invasion by K. pneumoniae and S. typhi. Interference with receptor-mediated endocytosis by g-strophanthin or monodansylcadaverine and inhibition of endosome acidification by monensin reduced the number of viable intracellular K. pneumoniae cells, but not S. typhi cells. The depolymerization of microfilaments by cytochalasin D inhibited the uptake of both bacteria. Microtubule depolymerization caused by colchicine, demecolcine, or nocodazole and the stabilization of microtubules with taxol reduced only the invasion ability of K. pneumoniae. S. typhi invasion was unaffected by microtubule depolymerization or stabilization. These data suggest that the internalization mechanism triggered by K. pneumoniae 3091 is strikingly different from the solely microfilament-dependent invasion mechanism exhibited by many of the well-studied enteric bacteria, such as enteroinvasive Escherichia coli, Salmonella, Shigella, and Yersinia strains.

Characterization of the Chlamydia trachomatis vacuole and its interaction with the host endocytic pathway in HeLa cells

Chlamydia trachomatis, an obligate intracellular parasite and a major human pathogen, invades eukaryotic host cells and replicates within a membrane-bound compartment (termed the vacuole or inclusion) in the cytoplasm of the host cell. In this report, we describe in detail the characteristics of the vacuole throughout the chlamydial life cycle in terms of the endocytic pathway, as determined by epifluorescent and confocal immunofluorescence microscopy. By indirect immunofluorescence, the transferrin receptor (TfR), a component of early endosomes, and the cation-independent mannose-6-phosphate receptor (CI-M6PR), a component of late endosomes, were found in close association with the chlamydial vacuole as early as 4 h postinfection (hpi) and as late as 20 hpi. Fluorescein isothiocyanate (FITC)-labeled Tf was also found to colocalize with the vacuole at 4, 12, and 20 hpi, indicating that exogenously added ligands can be transported to the region of the vacuole. Antibodies to several different lysosomal proteins failed to label the chlamydial vacuole at any time point during the life cycle. Indirect immunofluorescence of cells infected with chlamydiae stained with an antibody to the trans-Golgi network (TGN) protein TGN38 demonstrated that in infected cells, the integrity and structure of the TGN was altered. The rates of Tf recycling in infected and uninfected cells were compared by fluorescence microscopy and quantitated with 125I-Tf. While the rate of FITC-Tf recycling from endocytic compartments in chlamydia-infected cells did not appear different from that of uninfected cells, a small pool of FITC-Tf that had accumulated adjacent to the chlamydial vacuole recycled at a slower rate. Quantitation of Tf recycling with 125I-Tf showed that Tf was recycled more slowly in infected cells than in uninfected cells. The altered distribution of several endocytic pathway markers and the slowed Tf recycling are consistent with the hypothesis that the chlamydial vacuole interacts with the endocytic pathway of the host. These results furthermore suggest that the chlamydial vacuole does not correspond to a canonical endocytic compartment but that it is a unique and dynamic organelle that shares several characteristics with recycling endosomes of the host cell. Interactions with the early and/or late endosomal compartments, in addition to the Golgi apparatus, may provide a source of membrane or nutrients for the replicating organisms.

Vesicles containing Chlamydia trachomatis serovar L2 remain above pH 6 within HEC-1B cells

Chlamydia trachomatis serovar L2 is an obligate intracellular bacterium which is internalized in target epithelial cells by endocytosis and resides within a membrane-bound vesicle. Over the next several hours following entry, individual serovar L2-containing vesicles fuse with one another to form a single membrane-bound vesicle (or inclusion) within which the microcolony develops. The experiments reported here directly examined the pH of vesicles containing chlamydiae. The pH was determined by measuring emission ratios of the fluorescent, pH-sensitive probe SNAFL (5-[and 6-]-carboxyseminaphthofluorescein-1, succinimidyl ester) conjugated to chlamydiae. The pH remained above 6.0 at 2, 4, and 12 h after infection, while the pH of vesicles contained heat-killed organisms fell 5.3. In the presence of amines, which raise the pH of acidic compartments, C. trachomatis inclusion formation was unaffected. Inactivation of Na+,K+ -ATPases, the ion pumps responsible for maintaining a pH above 6 within early endocytic vesicles, inhibited the growth of C. trachomatis within epithelial cells. Preventing vesicular acidification by inhibiting the vacuolar proton ATPase did not affect chlamydial growth. Thus, chlamydiae do not reside within highly acidic vesicles and avoid the pathway leading to lysosomes.

Differential interaction with endocytic and exocytic pathways distinguish parasitophorous vacuoles of Coxiella burnetii and Chlamydia trachomatis

Coxiella burnetii and Chlamydia trachomatis are bacterial obligate intracellular parasites that occupy distinct vacuolar niches within eucaryotic host cells. We have employed immunofluorescence, cytochemistry, fluorescent vital stains, and fluid-phase markers in conjunction with electron, confocal, and conventional microscopy to characterize the vacuolar environments of these pathogens. The acidic nature of the C. burnetii-containing vacuole was confirmed by its acquisition of the acidotropic base acridine orange (AO). The presence of the vacuolar-type (H+) ATPase (V-ATPase) within the Coxiella vacuolar membrane was demonstrated by indirect immunofluorescence, and growth of C. burnetii was inhibited by bafilomycin A1 (Baf A), a specific inhibitor of the V-ATPase. In contrast, AO did not accumulate in C. trachomatis inclusions nor was the V-ATPase found in the inclusion membrane. Moreover, chlamydial growth was not inhibited by Baf A or the lysosomotropic amines methylamine, ammonium chloride, and chloroquine. Vacuoles harboring C. burnetii incorporated the fluorescent fluid- phase markers, fluorescein isothiocyanate-dextran (FITC-dex) and Lucifer yellow (LY), indicating trafficking between that vacuole and the endocytic pathway. Neither FITC-dex nor LY was sequestered by chlamydial inclusions. The late endosomal-prelysosomal marker cation-independent mannose 6-phosphate receptor was not detectable in the vacuolar membranes encompassing either parasite. However, the lysosomal enzymes acid phosphatase and cathepsin D and the lysosomal glycoproteins LAMP-1 and LAMP-2 localized to the C. burnetii vacuole but not the chlamydial vacuole. Interaction of C. trachomatis inclusions with the Golgi-derived vesicles was demonstrated by the transport of sphingomyelin, endogenously synthesized from C6-NBD-ceramide, to the chlamydial inclusion and incorporation into the bacterial cell wall. Similar trafficking of C-NBD-ceramide was not evident in C. burnetii-infected cells. Collectively, the data indicate that C. trachomatis replicates within a nonacidified vacuole that is disconnected from endosome-lysosome trafficking but may receive lipid from exocytic vesicles derived from the trans-Golgi network. These observations are in sharp contrast to those for C. burnetii, which by all criteria resides in a typical phagolysosome.

Adherence to and invasion of tissue culture cells by Vibrio hollisae

The adherence to and invasion of cultured epithelial cells by Vibrio hollisae were examined by quantitative studies and by light, fluorescent, and electron microscopy. Condensed actin was observed around clustered adherent and intracellular bacteria. Bacteria multiplied intracellularly. Inhibitor studies indicated that internalization occurred by an integrated pleiotropic process involving eukaryotic and prokaryotic protein syntheses, microfilaments, microtubules, and receptor-mediated endocytosis.

Low-efficiency (macro-)pinocytic internalization of non-pathogenic Escherichia coli into HEp-2 cells

HEp-2 cells internalize non-pathogenic Escherichia coli bacteria by a low-efficiency internalization mechanism which is upregulated in Pho-derepressed strains (as shown by Sinai and Bavoil in 1993), and is independent of microfilament integrity but requires functional microtubules. Here, we further characterize the microtubule requirement of this pathway using various effectors of microtubule integrity and function. Furthermore, we show that internalization is enhanced upon treatment with monodansylcadaverine, a specific inhibitor of receptor mediated endocytosis, and is insensitive to brefeldin A, which promotes the microtubule-dependent reorganization of the endosome. An assay system is also described to directly evaluate the contribution of pinocytosis to this pathway based on the ability of the bacteria to cointernalize and consequently colocalize with the fluid-phase marker, Texas-red-conjugated dextran (TRD). Using this assay, Hoescht-stained bacteria were observed in TRD-containing vesicles in numbers that are consistent with their observed internalization rate. Overall, these data are strongly supportive of the existence of a low-efficiency macropinocytic mechanism of entry for these non-pathogenic bacteria. Moreover, the observed requirements for host tyrosine kinase and protein kinase C activities suggest that it is inducible.

Interaction of outer envelope proteins of Chlamydia psittaci GPIC with the HeLa cell surface

The chlamydial life cycle involves the intimate interaction of components of the infectious elementary body (EB) surface with receptors on the susceptible eukaryotic cell plasma membrane. We have developed an in vitro ligand binding assay system for the identification and characterization of detergent-extracted EB envelope proteins capable of binding to glutaraldehyde-fixed HeLa cell surfaces. With this assay, the developmentally regulated cysteine-rich envelope protein Omp2 of Chlamydia psittaci strain guinea pig inclusion conjunctivitis was shown to bind specifically to HeLa cells. HeLa cells bound Omp2 selectively over other cell wall-associated proteins, including the major outer membrane protein, and the binding of Omp2 was abolished under conditions which alter its conformation. Furthermore, trypsin treatment, which reduces EB adherence, resulted in the proteolytic removal of a small terminal peptide of Omp2 at the EB surface and inactivated Omp2 in the ligand binding assay, while having a negligible effect on the major outer membrane protein. Collectively, our results suggest that Omp2 possesses the capacity to engage in a specific interaction with the host eukaryotic cell. We speculate that, since Omp2 is present only in the infectious EB form, the observed in vitro interaction may be representative of a determining step of the chlamydial pathogenic process.

Role of Ca2+ and calmodulin in ehrlichial infection in macrophages

Replication of Ehrlichia risticii was inhibited in P388D1 cells and murine peritoneal macrophages when a calmodulin antagonist (W-7, chlorpromazine, or trifluoperazine); a Ca2+ channel blocker (verapamil, diltiazem, nifedipine, or flunarizine); an extracellular Ca2+ chelator, EGTA [ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid]; an inhibitor of intracellular Ca2+ mobilization, TMB-8; or Ca2+ ionophore A23187 was added after internalization of the organism at 3 h postincubation. When intracellular ehrlichiae at their logarithmic stage of growth were treated with these reagents, not only was further proliferation prevented but also there was significant reduction in numbers of intracellular ehrlichiae. These reagents prevented spreading of E. risticii from P388D1 cells to THP-1 cells. None of these reagents prevented binding of [35S]methionine-labeled E. risticii to P388D1 cells, but all of these reagents prevented internalization of [35S]methionine-labeled E. risticii. Protein kinase C inhibitors, H-7 and staurosporin, had no effect. 14CO2 production from L-[14C]glutamine in Percoll-density-gradient-purified E. risticii was inhibited by A23187 but not by W-7 or verapamil, suggesting that Ca2+ but not calmodulin directly regulates ehrlichials glutamine oxidation. Pretreatment of E. risticii with W-7 or verapamil did not reduce its infectivity. These results indicate that calmodulin and Ca2+ are essential for ehrlichial internalization, replication, and spreading in macrophages but are not essential for binding.

Cytoskeletal requirements in Chlamydia trachomatis infection of host cells

Infection of genital epithelial cells by the closely related sexually transmitted pathogens Chlamydia trachomatis serovars E and L2 results in different clinical disease manifestations. Following entry into target host cells, individual vesicles containing chlamydiae fuse with one another to form one large inclusion. At the cellular level, the only obvious difference between these serovars is the time until inclusion maturation, which is 48 h for the invasive serovar L2 and 72 h for serovar E. To begin to define the intracellular events of these pathogens, the effect of cytoskeletal disruption on early endosome fusion and inclusion development in epithelial (HEC-1B) and fibroblast (McCoy) cells was analyzed by fluorescence microscopy. Disruption of microfilaments with cytochalasin D markedly reduced serovar E, but not serovar L2, infection of both cell lines. Conversely, microfilament as well as microtubule disruption, with colchicine or nocodazole, had no effect on serovar E inclusion development but resulted in the formation of multiple serovar L2 inclusions per cell during early and mid-development. Later in serovar L2 inclusion development (> 36 h postinfection), vesicles containing chlamydiae fused to form one large inclusion in the absence of an intact cytoskeleton. These results imply that (i) C. trachomatis serovar E may utilize a different pathway for uptake and development from serovar L2; (ii) these differences are consistent in both epithelial cells and fibroblasts; and (iii) the cytoskeleton plays a unique role in the infection of host cells by these two genital pathogens.

Some structures and processes of human epithelial cells involved in uptake of enterohemorrhagic Escherichia coli O157:H7 strains

Several enterohemorrhagic Escherichia coli (EHEC) strains of serotype O157:H7 isolated from patients with hemorrhagic colitis, ischemic colitis, or hemolytic uremic syndrome were all found to be able to invade certain human epithelial cell lines in vitro. Their ability to gain entry into epithelial cells was compared with those of known invasive Shigella flexneri and Salmonella typhi strains and the noninvasive E. coli strain HB101 in invasion assays utilizing gentamicin to kill extracellular bacteria. All EHEC strains under investigation were efficiently internalized into T24 bladder and HCT-8 ileocecal cells. In striking contrast to shigellae, the same EHEC strains were not taken up into human embryonic intestinal INT407 cells or HEp-2 cells any more than the noninvasive E. coli strain HB101. The mechanism(s) of EHEC internalization was characterized by comparing the invasion efficiencies in the absence and presence of a variety of inhibitors acting on structures and processes of prokaryotic or eukaryotic cells. Also, wild-type, plasmid-containing EHEC strains were compared with their plasmid-cured isogenic derivative strains to determine if plasmid genes affect invasion ability. Plasmid-cured EHEC invaded as well as wild-type EHEC, indicating that invasion ability is chromosomally encoded. Inhibition of bacterial protein synthesis by simultaneous addition of bacteria and chloramphenicol to the monolayer blocked EHEC uptake dramatically, suggesting the presence of an invasion protein(s) with a short half-life. Studies utilizing inhibitors which act on eukaryotic cells demonstrated a strong dependence on microfilaments in the process of uptake of all EHEC strains into both T24 and HCT-8 cells. In general, depolymerization of microtubules as well as inhibition of receptor-mediated endocytosis reduced the efficiency of EHEC invasion of T24 cells, whereas interference with endosome acidification reduced EHEC entry into only HCT-8 cells. Taxol-induced stabilization of microtubules did not inhibit internalization into T24 cells or into the HCT-8 cell line. In marked contrast, the ability of S. typhi Ty2 to invade either cell line was inhibited only by depolymerization of microfilaments. In addition to the cell line specificity of EHEC invasion, not all EHEC strains displayed uniform behavior in the presence of inhibitors, suggesting the existence of variant uptake pathways in different strains. Most importantly, previous reports of the inability of EHEC to invade INT407 or HEp-2 cell lines support the currently held belief that EHEC strains are noninvasive.(ABSTRACT TRUNCATED AT 400 WORDS)

Characterization of Ehrlichia risticii binding, internalization, and proliferation in host cells by flow cytometry

The binding, internalization, and proliferation of Ehrlichia risticii in P388D1 cells and equine polymorphonuclear (PMN) leukocytes were studied by immunofluorescent staining and flow cytometric analysis. The binding of ehrlichiae to P388D1 cells at 4 degrees C was dose dependent, and the antigens of bound organisms were susceptible to pronase treatment. Additionally, the binding of ehrlichiae to P388D1 cells was diminished when either P388D1 cells or ehrlichiae were treated with 1% paraformaldehyde for 30 min or 0.25% trypsin for 15 min. These results indicate that the ehrlichial ligand and host cell receptor are likely surface proteins. Following incubation at 37 degrees C, bound E. risticii and/or its antigens were removed with pronase and indirect immunofluorescent staining in the presence of saponin was used to examine intracellular ehrlichiae. Our results indicate that E. risticii was internalized into P388D1 cells within 3 h and proliferated by 48 h of incubation. The microfilament-disrupting agent cytochalasin D and the transglutaminase inhibitor monodansylcadaverine were used to differentiate between phagocytosis (sensitive to cytochalasin) and receptor-mediated endocytosis (sensitive to monodansylcadaverine) of E. risticii by P388D1 cells. In concentrations that produced distinctive morphological changes and inhibited phagocytosis of polystyrene latex beads, cytochalasin D did not suppress the infectivity of E. risticii. Binding, internalization, or proliferation of E. risticii was not affected by cytochalasin D. However, monodansylcadaverine inhibited infection of E. risticii in a dose-dependent manner. The agent did not affect the attachment of ehrlichiae to host cells, but it did suppress internalization and proliferation. These results suggest that E. risticii is internalized by receptor-mediated endocytosis and that productive infection by E. risticii does not depend on phagocytosis by the P388D1 cells. Although E. risticii did not bind to the surface of equine PMN leukocytes at 4 degrees C, organisms were taken up by this cell at 37 degrees C. E. risticii, however, failed to survive in equine PMN leukocytes.

Roles of Ca2+ and F-actin in intracellular aggregation of Chlamydia trachomatis in eucaryotic cells

The effect of intracellular free Ca2+ ([Ca2+]i) on the intracellular aggregation of Chlamydia trachomatis serovars L2 and E in McCoy and HeLa cells is investigated. Loading the cells with the Ca2+ chelator MAPT/AM (1,2-bis-5-methyl-amino-phenoxylethane-N,N-n'-tetra-acetoxymethyl acetate), thereby decreasing the [Ca2+]i from 67 to 19 nM, decreased the number of cells with a local aggregation of chlamydiae in a dose-dependent manner. Neither the attachment nor the uptake of elementary bodies (EBs) was, however, affected after depletion of Ca2+ from the cells. There was no significant difference in the level of measured [Ca2+]i between infected and uninfected cells. Reducing the [Ca2+]i also significantly inhibited chlamydial inclusion formation. Differences in the organization of the actin filament network were observed in response to [Ca2+]i depletion. In Ca(2+)-depleted cells, where few EB aggregates were formed, few local accumulations of F-actin were observed in the cytosol. These results suggest that the aggregation of EBs in eucaryotic cells requires a normal homeostasis of intracellular Ca2+. By affecting F-actin reorganization and putatively certain Ca(2+)-binding proteins, [Ca2+]i plays a vital role in the infectious process of chlamydiae.

Binding of Chlamydia trachomatis serovar L2 to collagen types I and IV, fibronectin, heparan sulphate, laminin and vitronectin

Chlamydia trachomatis serovar L2 elementary bodies were tested for binding to 125I-labelled components of the extracellular matrix. C. trachomatis bound high levels of collagen type I and heparan sulphate, whereas the binding to collagen type IV, fibronectin, laminin and vitronectin was substantially less. Preliminary characterization showed that chlamydial surface proteins are essential for binding to occur. Our results suggest that a selective affinity for C. trachomatis to a limited number of components of the extracellular matrix may have important implications mediating attachment to host cell surfaces and localization of chlamydiae in other tissues, such as joints.

Mechanism of C. trachomatis attachment to eukaryotic host cells

A novel trimolecular mechanism of microbial attachment to mammalian host cells was characterized for the obligate intracellular pathogen Chlamydia trachomatis. Using purified glycosaminoglycans (GAGs) and specific GAG lyases, we demonstrated that a heparan sulfate-like GAG present on the surface of chlamydia organisms is required for attachment to host cells. These observations were supported by inhibition of attachment following binding of heparan sulfate receptor analogs to chlamydiae and by demonstrating that chlamydiae synthesize a unique heparan sulfate-like GAG. Furthermore, exogenous heparan sulfate, as an adhesin analog, restored attachment and infectivity to organisms that had lost these attributes following treatment with heparan sulfate lyase. These data suggest that a GAG adhesin ligand mediates attachment by bridging mutual GAG receptors on the host cell surface and on the chlamydial outer membrane surface.

Mobilization of F-actin and clathrin during redistribution of Chlamydia trachomatis to an intracellular site in eucaryotic cells

Immunofluorescence was used to examine the distribution of Chlamydia trachomatis serovars L2 and E, F-actin, and clathrin in infected McCoy and HeLa cells. After incubation at 4 degrees C, C. trachomatis serovar L2 was randomly distributed on the McCoy cell surface. After a temperature shift to 37 degrees C, chlamydiae redistributed, within 30 min, to one local aggregate in the central or perinuclear region of individual cells. About 90% of these aggregated chlamydiae were intracellularly localized, but some remained randomly distributed on the cell surface. Similar results were obtained with HeLa cells and C. trachomatis serovar E, except that the redistribution was slower in HeLa cells than in McCoy cells and fewer cells infected with serovar E exhibited a local aggregate than those infected with serovar L2. Cytochalasin D inhibited more than 90% of this local aggregation. Instead, in cytochalasin D-treated cells, the entry of chlamydiae was inhibited and the organisms became localized on the cell surface in a peripheral local aggregate that distributed in a manner similar to that of phalloidin-stained actin. In a double immunofluorescence assay, F-actin and clathrin aggregated correspondingly in time and position with central or perinuclear aggregation of chlamydiae. These results indicate that polymerized actin and clathrin participate in a rapid redistribution of chlamydiae to an intracellular aggregate.

Recombinant Escherichia coli clones expressing Chlamydia trachomatis gene products attach to human endometrial epithelial cells

To identify Chlamydia trachomatis genes involved in attachment to host cells, a chlamydial genomic library was screened on the basis of binding characteristics by two methods. In the whole-cell screen, individual recombinant Escherichia coli clones were assayed for adherence to eukaryotic cells. In the membrane-binding screen, each recombinant colony of E. coli was treated with CHCl3 and assayed for binding to purified, 3-[(3-cholamidopropyl)-dimethyl-ammonio]-1-propanesulfonate (CHAPS)-solubilized, 35S-labeled eukaryotic membrane material. Initial screening with McCoy cells was refined by using HEC-1B cells, a human endometrial epithelial cell line, which discriminate among recombinants adhering to McCoy cells. Some recombinants demonstrate significantly greater adherence to HEC-1B cells than to McCoy cells and appear, by transmission electron microscopy, to associate with electron-dense areas of the epithelial cell plasma membrane, resembling coated pits. Recombinants positive by one or both screening methods were examined by Southern and Western (immunoblot) analyses, which revealed the presence of chlamydial sequences inserted in the plasmids and the expression of novel 18-, 28-, and approximately 82 kDa, and perhaps of 18 Maxicell analysis of selected recombinants confirmed that the proteins of 28 and approximately 82 kDa, and perhaps of 18 kDa, are plasmid encoded. Antiserum generated against the recombinant approximately 82-kDa protein reacted in Western analysis with a similar-sized protein from C. trachomatis serovar E elementary bodies (EB) and reticulate bodies, serovar L2 EB, and C. psittaci EB. E. coli JM109(pPBW58) contains a 6.7-kb plasmid insert which encodes proteins of all three sizes. Under a number of different conditions in the whole-cell attachment assay--i.e., at 4 degrees C, in Ca(2+)- and Mg(2+)-free medium, in the presence of trypsin or dextran sulfate, and with rabbit aortic endothelial cells--the binding specificity of JM109(pPBW58) parallels that of C. trachomatis EB. Finally, the adherence phenotype of E. coli JM109(pPBW58) correlates directly with the presence of the recombinant plasmid; the phenotype is lost concurrently with loss of the recombinant plasmid, and the into E. coli JM109. The role of the 18-, 28-, and approximately 82-kDa proteins in mediating attachment, whether they act in concert as a complex or individually, has yet to be determined.

Interaction of chlamydiae and host cells in vitro

The obligately intracellular bacteria of the genus Chlamydia, which is only remotely related to other eubacterial genera, cause many diseases of humans, nonhuman mammals, and birds. Interaction of chlamydiae with host cells in vitro has been studied as a model of infection in natural hosts and as an example of the adaptation of an organism to an unusual environment, the inside of another living cell. Among the novel adaptations made by chlamydiae have been the substitution of disulfide-bond-cross-linked polypeptides for peptidoglycans and the use of host-generated nucleotide triphosphates as sources of metabolic energy. The effect of contact between chlamydiae and host cells in culture varies from no effect at all to rapid destruction of either chlamydiae or host cells. When successful infection occurs, it is usually followed by production of large numbers of progeny and destruction of host cells. However, host cells containing chlamydiae sometimes continue to divide, with or without overt signs of infection, and chlamydiae may persist indefinitely in cell cultures. Some of the many factors that influence the outcome of chlamydia-host cell interaction are kind of chlamydiae, kind of host cells, mode of chlamydial entry, nutritional adequacy of the culture medium, presence of antimicrobial agents, and presence of immune cells and soluble immune factors. General characteristics of chlamydial multiplication in cells of their natural hosts are reproduced in established cell lines, but reproduction in vitro of the subtle differences in chlamydial behavior responsible for the individuality of the different chlamydial diseases will require better in vitro models.

Effects of cytochalasin D and methylamine on intracellular growth of Legionella pneumophila in amoebae and human monocyte-like cells

A cloned and axenically cultured strain of Hartmannella vermiformis was used as a model to study intracellular multiplication of Legionella pneumophila in amoebae. The growth of L. pneumophilia in both H. vermiformis and a human monocyte-like cell line (U937) was investigated with cytoskeletal and metabolic inhibitors. L. pneumophila replicated only intracellularly in these cellular models, and electron microscopy showed ultrastructural similarities in the initial phase of multiplication. Treatment of amoebae with an inhibitor of microfilament-dependent phagocytosis (cytochalasin D, 0.5 or 1.0 micrograms/ml) did not inhibit intracellular growth of L. pneumophila; however, intracellular multiplication was inhibited by treatment of U937 monocytes with the same concentrations of cytochalasin D. Methylamine (10 to 100 mM), an inhibitor of adsorptive pinocytosis, inhibited the replication of L. pneumophila in amoebae in a dose-dependent manner. All doses of methylamine tested (10 to 50 mM) inhibited growth of L. pneumophila in U937 monocytes. Cytochalasin D and methylamine had no effect on the multiplication of L. pneumophila in culture medium or on the viability of amoebae or U937 monocytes. Intracellular replication of L. pneumophila in H. vermiformis may be accomplished by a cytochalasin D-independent mechanism, such as adsorptive pinocytosis. In contrast, both cytochalasin D- and methylamine-sensitive mechanisms may be essential for the intracellular multiplication of L. pneumophila in U937 monocytes.

Characterization of the cytochalasin D-resistant (pinocytic) mechanisms of endocytosis utilized by chlamydiae

The cytochalasin D-resistant (pinocytic) portion of the entry of two chlamydia strains (Chlamydia trachomatis L2/434/Bu and Chlamydia psittaci GPIC [guinea pig inclusion conjunctivitis]) was examined. By ultrastructural criteria, few organisms of either strain were observed in association with coated host-cell plasma membrane during entry into McCoy cells; this argues against a coated-pit mechanism of entry. When association with a coated membrane was seen, coat material appeared to pinch off ahead of internalizing chlamydiae. However, entry of both strains was substantially reduced by cytosol acidification, a procedure shown to prevent coated-pit vesiculation (K. Sandvig, S. Olsnes, O. W. Petersen, and B. van Deurs, J. Cell Biol. 105:679-689, 1987). No conclusive evidence of displacement of the fluid-phase marker [3H]sucrose from constitutively forming endocytic vesicles was found. Indeed the entry of strain 434 (but not strain GPIC) was accompanied by the influx of a large volume of fluid, suggesting an inducible mechanism. Additionally, entry of strain 434 (but not strain GPIC) was partially inhibitable by amiloride, yet the drug had no effect on the entry of transferrin, a ligand known to enter solely via coated pits. Our findings endorse the view that chlamydial entry can occur via a pathway involving coated pits. However, the unusual morphology of entry and lack of fluid exclusion are consistent with a process whereby although chlamydiae are not fully enclosed by coat material, their entry is dependent on the vesiculation of coated pits. Furthermore, the data support the proposition that a significant proportion of the entry of strain 434 occurs via an inducible pathway independent of coated-pit uptake.

Fusion of inclusions following superinfection of HeLa cells by two serovars of Chlamydia trachomatis

We used a double-label immunofluorescence assay to examine the ability of Chlamydia trachomatis serovar F to infect and develop within HeLa 229 cells previously infected with serovar E. No exclusion to superinfection occurred for up to 24 h following infection by serovar E. The percentage of HeLa cells infected in cultures inoculated with both strains was identical to that of cells in cultures inoculated with one strain as a control. Organisms of both serovars were located within the same intracellular inclusion in 88 to 95% of HeLa cells infected with both serovars. The proportion of superinfected HeLa cells containing both strains in separate inclusions increased when there was exposure to inhibitors of cytoskeletal structure and transport. We used this inhibition to demonstrate that fusion of C. trachomatis phagosomes occurs throughout the developmental cycle.

Entry of genital Chlamydia trachomatis into polarized human epithelial cells

To study the initial invasion process(es) of genital chlamydiae, a model system consisting of hormonally maintained primary cultures of human endometrial gland epithelial cells (HEGEC), grown in a polarized orientation on collagen-coated filters, was utilized. After Chlamydia trachomatis inoculation of the apical surface of polarized HEGEC, chlamydiae were readily visualized, by transmission electron microscopy, in coated pits and coated vesicles. This was true for HEGEC maintained in physiologic concentrations of estrogen (proliferative phase) and of estrogen plus progesterone (secretory phase), despite the finding that association of chlamydiae with secretory-phase HEGEC is significantly reduced (P = 0.025; A.S. Maslow, C.H. Davis, J. Choong, and P.B. Wyrick, Am. J. Obstet. Gynecol. 159:1006-1014, 1988). In contrast, chlamydiae were rarely observed in the clathrin-associated structures if the HEGEC were cultured on plastic surfaces. The same pattern of coated pit versus noncoated pit entry was reproducible in HeLa cells. The quantity of coated pits associated with isolated membrane sheets derived from HeLa cells, grown on poly-L-lysine-coated cover slips in medium containing the female hormones, was not significantly different as monitored by radiolabeling studies and by laser scanning microscopy. These data suggest that culture conditions which mimic in vivo cellular organization may enhance entry into coated pits for some obligate intracellular pathogens.

Flow cytometric analysis of Chlamydia trachomatis interaction with L cells

Immunofluorescent staining and flow cytometric analysis have been investigated as means of studying the early stages of in vitro infection of Chlamydia trachomatis. The lymphogranuloma venereum strain of C. trachomatis was grown in vitro in L cells, fixed in p-formaldehyde, stained with fluorescein isothiocyanate (FITC)-conjugated monoclonal antibody to the chlamydial major outer membrane protein, and analyzed flow cytometrically. Infected cells stained 50-100 times more intensely than uninfected cells, and they could easily be discriminated by flow analysis. The number of infected cells and the fluorescence intensity of individual cells were proportional to the multiplicity of infection. The attachment of purified elementary bodies to L cells could be analyzed by immunofluorescence and flow cytometry. Cells exposed to 0.26 inclusion-forming units/cell could be discriminated from an unexposed population. Flow analysis of purified elementary bodies was possible after fluorescent staining with the aid of a laser-based cytometer and gating on low volume.

Ultrastructural study of mode of entry of Chlamydia psittaci into L-929 cells

The entry of Chlamydia psittaci into L-929 cells was studied morphologically by transmission electron microscopy and quantitatively by a method that discriminates between attachment and uptake. Upon adsorption of 3H-labeled elementary bodies (EBs) to host cells at 4 degrees C, the EBs bound efficiently to the L-cell surface. Binding reached an equilibrium level of 55% in 3 h. Ultrastructural analysis revealed that EBs were bound preferentially to the tips and sides of microvilli at this temperature. The EBs were also observed in coated pits located at the bases of microvilli and along smooth surfaces of the host cell. No internalization was observed at 4 degrees C. When cells with prebound 3H-labeled EBs were warmed to 37 degrees C, the EBs rapidly became resistant to proteinase K removal (half time = 5 min), indicating ingested chlamydiae. At 37 degrees C, the EBs were internalized within tightly bound vesicles surrounded by an electron-dense coat of fibrillar material. EBs were also present in smooth-surfaced pits and vesicles of the host cell. Using alpha 2-macroglobulin coupled to colloidal gold (a known marker for receptor-mediated endocytosis), we observed that the entry of EBs into cells via coated pits was identical in appearance to the internalization of alpha 2-macroglobulin. Also, when the two ligands were mixed together, they could be seen within the same coated pits and were cointernalized within endocytic vesicles of the host cell. These results suggest that C. psittaci can enter nonprofessional phagocytic cells by a pathway which is similar to that of receptor-mediated endocytosis of many physiologically important macromolecules, bacterial toxins, and viruses.

Identification and properties of chlamydial polypeptides that bind eucaryotic cell surface components

An electroblotting technique was used to identify proteins of Chlamydia that bound surface-radioiodinated and Triton X-100-solubilized HeLa cell extracts. Two proteins, with apparent molecular masses of 18 and 32 kilodaltons (kDa), that bound HeLa cell surface components were identified on Chlamydia trachomatis L2 elementary bodies (EBs). Radioiodinated heparin, which disrupts chlamydial association with cultured cells, was also bound by these proteins. These two proteins were found on EBs but were absent or were present in reduced amounts on the noninfectious reticulate bodies. All C. trachomatis strains tested displayed two such proteins, although the apparent molecular weight of the larger protein varied with serotype in correlation with biotype and the disease that it caused. Two Chlamydia psittaci strains examined displayed only a single binding protein in the range of 17 to 19 kDa. All of the binding proteins stained intensely and distinctively on silver-stained sodium dodecyl sulfate-polyacrylamide gels and displayed an unusual sensitivity to reducing agents. The 32-kDa protein was not seen and did not bind 125I-labeled HeLa cell components if the EBs were solubilized in the presence of 2-mercaptoethanol. The 32-kDa protein was not affected by dithiothreitol, however. Similar to the effect of 2-mercaptoethanol, the 32-kDa protein was not visualized after treatment of EBs with the protease inhibitors tosyl-phenylalanine chloromethyl ketone (TPCK) or tosyl-lysine chloromethyl ketone (TLCK). TPCK and TLCK also abolished infectivity as did the alkylating agents N-ethylmaleimide and iodoacetamide, yet the latter two agents did not affect the appearance of the 32-kDa protein. These proteins were not detected in immunoblots with either rabbit antisera to C. trachomatis L2 EBs or by serum from a patient with lymphogranuloma venereum. The role of these proteins in the interaction of chlamydiae with host cells is not clear, but the binding of eucaryotic cell surface components and heparin, presence only during the infectious stage of the life cycle, variation between serotypes in correlation with disease, and sensitivity to reducing agents or protease inhibitors, collectively, suggest a role for these proteins in parasite-host interactions.

Binding, ingestion, and multiplication of Chlamydia trachomatis (L2 serovar) in human leukocyte cell lines

We examined the ability of lymphoblastoid-myeloid cell lines to bind, ingest, and permit multiplication of Chlamydia trachomatis (L2 serovar). Four types of chlamydia-cell line interactions were observed: minimal bacterial binding; bacterial binding, followed by ingestion and high-level multiplication; bacterial binding, followed by ingestion but minimal multiplication; and bacterial binding, but minimal ingestion or replication. Our data demonstrate that at 37 degrees C in vitro the L2 serovar can both bind avidly to a cell without entering it and enter nonphagocytic cells but not grow.

Recent advances in Chlamydia trachomatis

Chlamydia trachomatis is an obligate intracellular energy parasitic bacterium with a genome of 660 X 10(6) daltons, possessing a plasmid and unique life cycle which includes the differentiation of the infective elementary body to a replicative reticulate body. C. trachomatis is the etiological agent of trachoma, which affects approximately 500 million people in developing countries. Recently it became evident that in industrialised Western nations certain strains of C. trachomatis are the most common cause of sexually transmitted infections such as non-gonococcal urethritis, cervicitis, endometritis, salpingitis and subsequent ectopic pregnancies or infertility, perihepatitis, neonatal conjunctivitis and pneumonia, adult conjunctivitis and epididymitis. Since C. trachomatis infections are often asymptomatic, widespread screening of sexually active young people is needed in order to initiate early antibiotic treatment which may prevent serious complications such as ectopic pregnancies and infertility. Development of sensitive and simple techniques for mass screening for detection of Chlamydia in excretions as well as techniques for detection of specific markers of chronic internal infections (such as Chlamydia specific IgA antibodies) is of great importance.

Effect of proteolytic cleavage of surface-exposed proteins on infectivity of Chlamydia trachomatis

The proteolytic cleavage of Chlamydia trachomatis LGV-434 surface proteins and resultant effects on infectivity and association with cultured human epithelial (HeLa) cells have been examined. Of several proteases examined, trypsin, chymotrypsin, and thermolysin extensively cleaved the chlamydial major outer membrane protein (MOMP). Two proteases, trypsin and thermolysin, cleaved the MOMP to the extent that monomeric MOMP was not detectable by immunoblotting with monospecific polyclonal antibodies. In the case of thermolysin, not even antigenic fragments were detected. Surprisingly, infectivity toward HeLa cells was not diminished. In addition, the association of intrinsically 14C-radiolabeled elementary bodies (EBs) with HeLa cells or their dissociation by proteinase K was not measurably affected by prior trypsinization of the EBs. Trypsinization of lactoperoxidase surface-iodinated elementary bodies demonstrated that most of the 125I-labeled surface proteins were cleaved. In all cases, however, a number of proteolytic cleavage fragments remained associated with the EB surface after surface proteolysis. When trypsinized EBs were electrophoresed under nonreducing conditions and immunoblotted with either polyclonal or type-specific monoclonal MOMP antibodies, MOMP was found in a large oligomeric form that failed to enter the polyacrylamide stacking gel. Additionally, trypsinized viable EBs bound radioiodinated type-specific MOMP monoclonal antibody as efficiently as did the control nontrypsinized organisms. Taken together, the findings indicate that although the MOMP is highly susceptible to surface proteolysis, the supramolecular structure of the protein on the EB surface is apparently maintained by disulfide interactions. Thus, if surface-exposed chlamydial proteins are involved in the initial interaction of chlamydiae with eucaryotic cells, the functional domains of these proteins which mediate this interaction must be resistant to proteolysis and remain associated with the EB surface.

Attachment and internalization of a Chlamydia trachomatis lymphogranuloma venereum strain by McCoy cells: kinetics of infectivity and effect of lectins and carbohydrates

The kinetics of attachment and ingestion of Chlamydia trachomatis serotype L1 by monolayers of McCoy cells were studied by using a method that discriminated between attachment and uptake. When about 1% of the McCoy cells was infected, the proteinase K-resistant chlamydial fraction, regarded as ingested chlamydiae, reached a constant value after about 3 h of incubation at 37 degrees C. Uptake of chlamydiae at 4 degrees C could not be demonstrated. The attached and ingested chlamydial fractions were constant over an eightfold increase in chlamydial inoculum. Chitobiose and chitotriose, the di- and trisaccharides of N-acetyl-D-glucosamine, reduced the association of C. trachomatis serotype L1 with McCoy cells. Higher concentrations of chitobiose also selectively inhibited ingestion of chlamydiae. A corresponding effect of chitobiose was also observed on the number of chlamydial inclusions. Wheat germ agglutinin, specific for N-acetyl-D-glucosamine residues, reduced the association of chlamydiae when incubated at 4 degrees C, but not at 37 degrees C. A small inhibiting effect of concanavalin A on association of chlamydiae, but no effect of the corresponding carbohydrates, indicates a nonspecific effect on chlamydial attachment of this lectin. These results suggest that beta 1 leads to 4-linked oligomers of N-acetyl-D-glucosamine are important in the specificity of attachment of C. trachomatis to McCoy cells.